Rôle de Pinhead lors de la mise en place de l’axe dorso-ventral chez l’oursin Paracentrotus Lividus

Dorsal-ventral patterning is an important process during development in bilaterians and relies on an interplay between secreted BMP factors and their antagonists produced in two opposite signaling centers. Studies in Xenopus have shown that the dorsal and ventral signaling centers communicate each other to finely regulate the level of BMP signaling by using an autoregulatory expansion-repression circuit based on the activity of an atypical BMP called ADMP, whose transcription is repressed by BMP signaling. When BMP2/4 signaling decreases, admp expression increases and reactivates the BMP signaling pathway. The molecular mechanisms by which BMP signaling represses ADMP expression remain however, largely enigmatic. Recent studies in the tunicate Ciona intestinalis have uncovered a key role for the secreted factor Pinhead in this process. However, whether the function of Pinhead as a key regulator of admp expression is conserved in other species has never been investigated. To test if the role of Pinhead in mediating the repression of admp is conserved in echinoderms, we cloned the sea urchin pinhead and analyzed its spatiotemporal expression. Our results suggest that the positive regulation of pinhead by BMP signaling is not conserved in the sea urchin. We also perturbed the function of pinhead by injecting mRNA encoding Pinhead and antisense morpholino oligonucleotides targeting the pinhead transcript. Our results do not support the idea that Pinhead is a central regulator of admp expression in the sea urchin and suggest that additional mechanism likely account for the repression of pinhead by BMP signaling in this embryo.